In general, the sensor is used for measurement after it is coated with a layer referred to as a “receptor layer” which enables highly sensitive and selective detection of a sample molecule. The material used as a receptor layer includes various types such as molecular self-assembled monolayer, DNA/RNA, protein, antigen/antibody, or polymer. In addition to sensitivity and selectivity, from the viewpoint of reproducibility of measurement or durability of a sensor, the interaction between the receptor material and surface of the sensor with detection function (hereinbelow, simply referred to as the sensor surface) is important, and it is desired to have a stable binding state. For such reasons, it is necessary to perform the fixing of the receptor material under strictly controlled conditions. However, it is not easy to attain the optimized conditions. Furthermore, there is a problem in that the environment for measurement by the sensor is limited depending on the substance used for coating, e.g., a water soluble polymer cannot be used for measurement in water.
Regarding the sensor selectivity, it can be designed over a broad range including those with high specificity like an antigen-antibody reaction and those with broad-range selectivity like a polymer capable of adsorbing relatively various types of a sample depending on the substance used for coating. On the other hand, because there is no clear guideline set for the sensitivity, designing based on a clear guideline is not currently possible. Recently, regarding a sensor of the type by which stress applied on a surface is detected, it has been reported that physical parameters like membrane thickness or Young's modulus of a receptor material have a great influence as described in Non Patent Literatures 1 and 2. Specifically, in the case of Young's modulus being constant, there is a tendency that the sensitivity increases until the membrane thickness reaches a certain value and the sensitivity decreases thereafter. Based on this, for a molecular self-assembled monolayer, DNA/RNA, protein, or an antigen/antibody, increasing the membrane thickness is impossible per se, and thus it is not easy to achieve the improvement of sensitivity. In the case of a polymer, it is possible to increase the membrane thickness, but there is a problem related to solubility or weather resistance as described above. In view of the background described above, although there is a guideline for control·optimization of the sensitivity and selectivity of limited types of a sensor, the optimum substance for simultaneously satisfying them is not known yet. Thus, the discovery and demonstration of the substance are anticipated.